Apparatus for analyzing diluted and undiluted fluid samples

ABSTRACT

Ion chromatograms are prepared with a chromatograph including a separation column and a conductivity measuring ion detection unit which are adapted to be selectively placed in communication with separate reservoirs for diluted and undiluted samples of a fluid to be analyzed. A control unit switches the reservoirs into communication with an eluent pump for displacing fluid samples through the detection unit in timed relationship such that the most concentrated ion is measured in the diluted sample prior to measurement by the detection unit of the last of the lesser concentrated ions. A pump having a controllable flow rate is connected to a mixing conduit through control valves which switch the flow to and from the reservoirs so that the reservoirs may be simultaneously filled with diluted and undiluted samples of fluid. The diluted sample may be prepared by mixing the undiluted fluid with the eluent.

This is a division of application Ser. No. 07/130,831, filed Dec. 9,1987, now U.S. Pat. No. 4,872,992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an improved method of analyzing fluidsand an apparatus, such as an ion chromatograph, in which fluid samplesare automatically injected into a detection unit in both diluted andundiluted conditions for simultaneous determination of the concentrationof major and minor components of the fluid.

2. Background

Laboratory analysis of fluid samples in large numbers is carried outroutinely. For example, in the petroleum exploration and productionindustry the analysis of various brines obtained from sea water, groundwater and process samples are carried out with ion chromatographs andother spectrographic devices. The wide range of concentrations of theionized components often requires dilution of the fluid samples to makepossible the measurement of high concentrations of certain ions which,if the sample is not diluted, are present at concentrations beyond themeasurement range of the detector. In some instances, if a fluid sampleis not diluted before analysis, the major components cannot bequantified because they are present in concentrations beyond the linearresponse region of the detector device, the purity of recorded peaks ormaximum concentrations having large elution volumes is questioned due tothe tendency of adjacent peaks on the chromatogram to overlap as theconcentration of one or both components increase, or retention timescannot be used for identification purposes because of abnormal readingsand certain ion migration phenomena.

Conversely, if the fluid sample is diluted to lower the concentration ofthe so-called major ion components, one or more of the minor componentsto be measured cannot be reliably determined because theirconcentrations become close to or less than the limit of detection. As aresult, a two step analysis is required which can be very time consumingand expensive when large numbers of samples are required to be measured.Accordingly, the present invention is directed to improvements in ionchromatograph methods and systems for measuring the ion concentrationsin fluid samples, which improvements eliminate the need to prepare andinject into the chromatograph detection unit different standardsolutions or prepare and handle a particular fluid sample twice, namely,in both diluted and undiluted concentrations.

The desired results of the present invention include obtaining theconcentrations of all of the components of a fluid sample in a singlegraphic or numerical display such that a single chromatogram will showthe concentrations of all components. Accordingly, significant savingsin time for analyzing a particular type of fluid is realized by theimproved method and apparatus of the invention.

SUMMARY OF THE INVENTION

The present invention pertains to an improved apparatus and method foranalyzing the composition of a fluid sample wherein diluted andundiluted samples may be automatically prepared and essentiallysimultaneously analyzed.

In accordance with one aspect of the present invention, an improved ionchromatograph is provided wherein a fluid sample of a particularconcentration may be passed through a separation column and an iondetection unit and a diluted sample of the same fluid may also beautomatically prepared and injected through the separation column anddetection unit whereby the concentrations of the various ion componentsof the fluid may be measured and recorded substantially simultaneously.

In accordance with yet another aspect of the present invention, there isprovided a method and an improved apparatus for preparing a dilutedsample of a fluid composition to be analyzed wherein the sample dilutionmay be automatically controlled. Moreover, depending on the fluid samplebeing measured, the eluent and diluent may comprise the same fluid ininstances, for example, in analyzing various brine solutions.

Still further, the present invention provides an improved ionchromatograph wherein an arrangement of fluid conducting control valvesis configured to prepare and inject samples of fluid to an ionseparation column and an ion detection unit whereby the composition of afluid sample in both a diluted condition or an undiluted condition maybe recorded. The improved configuration of the chromatograph may beutilized in a conventional operating mode and in the improved operatingmode.

The present invention permits the simultaneous determination of majorand minor components of a fluid within a chromatograph operation timethat is less than the sum of the operating times required of prior artoperating modes. The improved operating mode not only saves time butrequires less computer data storage or memory capacity, does not requireany substantial new hardware or software, particularly when consideringa particular type of commercially available chromatograph, results insavings in the use of chemical reagents, when compared to other dilutionschemes, provides for switching between selected modes of operation, canbe used to preconcentrate very dilute fluid samples and has a wide rangeof applications. These and other advantages and desirable aspects of thepresent invention will be further appreciated by those skilled in theart upon reading the detailed description which follows in conjunctionwith the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of the improved fluid analysis apparatusor system of the present invention; and

FIGS. 2 through 4 are diagrams illustrating the measurement of ionconcentrations in a fluid sample in selected modes of operation inaccordance with the improved apparatus and method of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the description which follows and in the drawing conventionalelements are described in general terms and are shown in somewhatschematic form in the interest of clarity and conciseness.

In the analysis of brine solutions, for example, commercial ionchromatographs often require that a two step analysis be carried out tomeasure the presence of ions of high concentration as well as those ionsof lesser concentrations. For example, FIG. 2 represents a plot of theconductivity of various ions detected in a brine solution versus timewhen the solution is passed through an ion concentration column and aconductivity measuring type ion detection unit. In FIGS. 2 through 4 thescale of the ordinate is indicated in micro siemens and the abscissa istime in minutes. In FIG. 2, the concentration of the most highlyconcentrated ion is indicated by the peak 10 and is so great that theapparatus is not able to measure the concentration and the response ofthe detector is no longer linear. The concentrations of lesserconcentrated ions are, however, measurable as indicated by the peaks 12,14, 16 and 18. On the other hand, as shown in FIG. 3 a diluted sample offluid passed through the separation column and the detection unit mayonly be capable of detection of the most concentrated ion, as indicatedby the peak 20, while the lesser concentrated ions have been so dilutedthat they are not measurable by the conductivity measuring typedetection unit. Not only are two samples required to be independentlyprepared, loaded and injected into the apparatus, but the data output ofthe apparatus normally appears on two separate records or displays. Thepresent invention overcomes the problems associated with measuring thecompositions of fluids having relatively high concentrations ofparticular components and relatively low concentrations of othercomponents as will be appreciated by the further description herein.

FIG. 1 illustrates a somewhat simplified schematic diagram of amodified, commercially available ion chromatograph such as a Model 2120Ion Chromatograph manufactured by Dionex Corporation, Sunnyvale, Calif.The apparatus illustrated in FIG. 1 is generally designated by thenumeral 22 and includes power operated valves 24 and 26 which areadapted to be shifted simultaneously between their positions a andpositions b to in effect operate as one valve unit. The apparatus 22further includes power operated valves 28 and 30 which are also adaptedto operate as one valve simultaneously between their respectivepositions a and b.

The valve 24 is adapted to be in communication with a pump 32 forsupplying on a substantially continuous basis an eluent from a source34. The eluent may be a suitably deionized water treated with salts andacids of a type commercially available and appropriate for theparticular analysis to be carried out. The valve 30 is in communicationwith an ion separation column 36 comprising part of the above-identifiedcommercially available ion chromatograph. The column 36 may include asuppression column, not shown, depending on the eluent being used. Theseparation column 36 is connected to a valve 38 which is operablyconnected to a second valve 40 for simultaneous operation therewith tomove from respective positions a to positions b. The valves 38, 40 maybe constructed as an integral valve unit having the flow directingcapabilities indicated by the schematic diagram. The valve 38 isconnected to an ion detection unit 42 which may be of the relativeelectrical conductivity measurement type and which may be appropriatelyconfigured depending on the particular type of fluid being sampled. Thedetection unit 42 may also be part of the above-mentioned chromatograph.

As illustrated in FIG. 1, the valve 40 is in communication with thevalve 24 by way of a conduit 44 and the valves 38 and 40 are incommunication with each other by way of a tee fitting or conduit 46which is connected to fluid mixing means 48. The mixing means 48 may bea conduit coil having a plurality of turbulating devices disposedtherein such as a series of glass beads or other means which will resultin thorough mixing of fluid entering the mixing means 48 by way of thevalves 38 and 40. The mixing conduit 48 is connected to the valve 30 byway of a conduit 50. The valves 24 and 26 are also interconnected by aconduit 52 having a reservoir portion of predetermined volume and thevalves 28 and 30, making up a cooperable valve unit, are alsointerconnected by a conduit 54 having a reservoir portion ofpredetermined volume. The reservoir conduits 52 and 54 may be conduitsof specified length and cross sectional flow area interconnecting theirrespective ports of the valves 24 and 26 and the valves 28 and 30.

The valve 26 is operable to place the reservoir conduit 52 incommunication with a source of fluid to be sampled by way of a conduit58 and a pump 60. The pump 60 is adapted to have a programmablecontroller 62 whereby the displacement and flow rate of the pump may berelatively precisely controlled during operation of the apparatus 22.The pump 60 may, in fact, be a stepper motor driven syringe such asmodel 401 Dilutor manufactured by Gilson Medical Electronics Inc.,Middletown, Wis. The syringe controller may be of a type 212B alsomanufactured by Gilson Medical Electronics Inc. Fluid samples aresupplied to the pump 60 from a source 64 which may comprise an automaticfluid sampling device such as a model 32297 manufactured by DionexCorporation. The controller 62 and the valves 24, 26, 28, 30 and 38, 40may be controlled by a central processing unit 66 such as a Series 9000computer manufactured by Hewlett Packard Company. A suitable interface68 is adapted to convert computer command signals to appropriate signalsfor operating the controller 62 and the respective valves connected tothe interface. Signals indicating the conductivity of the fluid passingthrough the detection unit 42, or other means of detection, depending onthe type of detection unit used, are input to the computer 66 throughthe interface 68 and converted to readable diagrams which may bedisplayed on a printer 70 and having the format illustrated in FIGS. 2through 4.

The operation of the apparatus 22 and the methods of the presentinvention may be carried out in one of several ways as will now bedescribed. If it desired to measure an undiluted sample from the source64, the apparatus is first conditioned with the valves 24, 26, 28, 30,38 and 40 in their respective positions a as illustrated in FIG. 1. Thepump 32 continuously pumps eluent through conduit 33 to the separationcolumn 36 and the valve 38 and through the detection unit 42 to wastedischarge by way of conduit 43. The conduits 58, 52, the valves 24 and26, the conduit 44 and the valve 40 are suitably purged by fluid to besampled as the pump 60 is operated to fill the reservoir conduit 52 withthe sample to be analyzed. Fluid to be sampled is flushed through theportions of the system described above and discharged from the valve 40by way of waste conduit 41.

When it is desired to analyze a sample in the reservoir conduit 52,displacement of fluid through the conduit 58 by the pump 60 isterminated and the valves 24 and 26 are shifted to their positions bwhereby a sample in the conduit 52 is carried by the eluent in conduit33 through the separation column 36 and the detection unit 42 forrecording a chromatogram in accordance with conventional operation ofthe above-mentioned commercial chromatograph. During measurement in thisso-called standard mode, the valves 38 and 40 remain in their positionsa. The valves 28 and 30 remain in their positions a during the injectionof the sample from the reservoir conduit 52.

The apparatus 22 may also be utilized to conduct a so-called "online"chromatogram of a diluted sample of fluid from the source 64. Theapparatus 22 is conditioned for measurement of a diluted sample of fluidby placing the valves 24 and 26 in their positions a, the valves 28 and30 in their positions a and the valves 38 and 40 also in their positionsa while the pumps 32 and 60 are operated to purge the flow paths adaptedto receive the respective fluids with the valves in the above-mentionedpositions. The pumps 32 and 60 may be adjusted as to their flow rates toprovide the required dilution of the fluid from the source 64 with theeluent from the source 34 which is now used also as a diluent. When theflow rates of the pumps 32 and 60 have been adjusted the valves 38 and40 are shifted simultaneously to their positions b so that a fluidmixture is conducted through the tee 46 and the mixing conduit 48 and tothe reservoir conduit 54. After a predetermined time period whichprovides for complete filling of a thoroughly mixed or diluted solutionin the reservoir conduit 54 between valves 28 and 30, the valves 38 and40 are returned to their positions a. If necessary, the flow rate ofpump 32 is then adjusted to the eluent flow rate normally used for thedisplacement or injection of the fluid sample into the separation columnand the detection unit. When flow adjustment is completed and theseparation column 36 and detection unit 42 suitably flushed, the valves28 and 30 are shifted simultaneously to their positions b whereuponeluent from the pump 32 displaces the diluted fluid sample in thereservoir conduit 54 for injection into the separation column 36 and thedetection unit 42. Analysis of the diluted fluid sample is then carriedout in a conventional manner and the diluted sample recorded to yield achromatogram similar to that of FIG. 3, for example.

An improved method of determining the composition of major and minorcomponents of a fluid sample may be advantageously carried out using theapparatus 22 in yet another mode of operation. With the valves 24, 26,28, 30, 38 and 40 in their positions a, the pumps 32 and 60 are operatedto flush the system flow paths associated with the mentioned valvepositions. The combination of the valves 24 and 26 and the combinationof the valves 28 and 30 will be shifted from their respective positionsa to their respective positions b in a predetermined sequence to providea chromatogram as indicated in FIG. 4. For example, if a highlyconcentrated component, as indicated by the peak 80 in FIG. 4, is onewhich is given up early by the separation column 36 and detected by thedetection unit 42 and is followed by detection of the lesserconcentrated components indicated by the peaks 82, 84, 86 and 88, thenthe diluted sample can be passed through the separation column and thedetection unit at a predetermined time delay with respect to theinjection of the undiluted fluid sample so that a measurable peak forthe component having the highest concentration, as indicated by the peak90, may be superimposed on the chromatogram for the sample which was runin the undiluted mode whereby a complete chromatogram or record of theconcentrations of the diluted and undiluted samples are providedsimultaneously.

On the other hand, if the component of the fluid sample having thehighest concentration is detected late in the detection phase ofdetermining the components of the fluid sample, the diluted sample maybe injected to and through the separation column 36 and the detectionunit 42 before the injection of the undiluted sample. The timing of theinjection steps may, of course, be selectively controlled by the centralprocessing unit 66. By way of example, essentially simultaneousdetermination of the major and minor components of a fluid sample may becarried out in accordance with the following procedure. Assuming thatthe basic composition of a sample was known, and therefore the presenceof either early or late separated ions, the central processing unit 66would be instructed to effect control of shifting of the valve groups24, 26 and 28, 30 in a predetermined sequence. Prior to operation of theapparatus to perform the simultaneous chromatographic analysis all ofthe valves would be in their positions a and the pumps 32 and 60instructed to flush the associated fluid flow paths, accordingly.

Assuming that the diluted sample was to be injected after injection ofthe undiluted sample, the valves 24 and 26 would be shifted to positionb at a predetermined time when a sample had filled and thoroughlyflushed the reservoir conduit 52 whereby this sample would be injectedthrough displacement by the eluent through the valves 28 and 30, stillin their position a, the separation column 36, the valve 38 in itsposition a, and the detection unit 42. Subsequent to injection of theundiluted sample, the valves 24 and 26 would be shifted back to positiona and the valves 38 and 40 shifted to position b to commence preparationof the diluted samples by mixing an undiluted quantity of the fluid tobe measured with the eluent (now acting as a diluent) and loading of thethoroughly mixed and diluted sample into the reservoir conduit 54.

After a predetermined time when it is assured that a thoroughly mixeddiluted sample is in the reservoir conduit 54, the valves 28 and 30 areshifted to position b while the valves 38 and 40 are shifted back toposition a and the diluted sample is injected through the separationcolumn 36 and the detection unit 42. As mentioned previously, the timingof injection of a diluted fluid sample is controlled such that the mostconcentrated ion is recorded to provide a chromatogram of the typeillustrated in FIG. 4 wherein the diluted sample shows the concentrationof the most highly concentrated ion within the scale of thechromatogram. The chromatogram would be appropriately noted that aconversion factor should be applied to the peak 90 with respect to thescale of the ordinate in FIG. 4.

After analysis of an undiluted and a diluted sample is carried out allof the valves are returned to their positions a in preparation foranalysis of another sample by placing a sample source in flowcommunication with the pump 60. Repeated analysis of various samplesmay, of course, be substantially automated by control of the valves aswell as the pumps 32 and 60 by the central processing unit. The source64 may be an automatic sampling unit for placing various fluidquantities in communication with the pump 60, selected at will.Moreover, the apparatus illustrated in FIG. 1 may be modified to placethe detection unit 42 between the valve 38 and the separation column 36which does not affect the operation of the apparatus as described.

By providing and operating an apparatus, such as the apparatus 22,according to the method of the present invention, a substantial savingsin time is realized for analyzing the components of a fluid samplewherein a relatively high concentration of a particular component isexpected and would adversely affect the operation of the system withoutsuitable sample dilution. Moreover, a single chromatogram may beproduced in accordance with the method of the present invention whichprovides a record of all of the components of the fluid in question on asingle recording during a process which provides considerable timesavings.

EXAMPLE I

A chromatogram of a sample of subterranean formation water was obtainedhaving the characteristics indicated generally in FIGS. 2, 3 and 4. Achromatogram according to FIG. 2 was obtained from an undiluted sampleto determine the concentration of the following ions: bromide (peak 12),nitrate (peak 14), phosphate (peak 16) and sulphate (peak 18). It wasclear from the chromatogram of FIG. 2 that the chloride ion (peak 10)was not measurable in an undiluted sample. Accordingly, a secondchromatogram was obtained on a sample of the same fluid diluted 1:500with deionized water to determine the concentration of chloride asindicated by peak 20 in FIG. 3. A sample of the same fluid was then runto obtain an online chromatogram of the diluted and undiluted samples asindicated by FIG. 4 where the concentration of chloride in the dilutedsample is indicated by the peak 90. By changing the timing of theshifting of the valve groups 24, 26 and 28, 30 it is, of course,possible to move the chloride peak 90 to any location desirable on thechromatogram. In the online analysis of both the diluted and undilutedsample, the eluent had a composition of 2.8 mN Na₂ C0₃ / 0.8 mN NaHC0₃.A micromembrane suppressor column comprising a model 038019 manufacturedby Dionex Corporation was interposed in the flow path between theseparation column and the detection unit.

Clearly, from the foregoing, when the eluent can also be used as thediluent an additional time saving is realized. In those instances whenthe eluent and diluent must be separate compositions the apparatus 22may be modified to provide a separate source of diluent which may beplaced in communication with the mixing tee 46 by way of a separatevalve in place of or interposed between the valve 40 and the mixing tee.

Although certain preferred embodiments of the present invention havebeen described in some detail herein, those skilled in the art willrecognize that the analysis of diluted and undiluted fluid samples inaccordance with the invention may be carried out on apparatus other thanan ion chromatograph including one of the type identified herein.Moreover, various other substitutions and modifications may be made tothe apparatus and the method described without departing from the scopeand spirit of the invention as recited in the appended claims.

What is claimed is:
 1. Automated apparatus for measuring theconcentration of ion oomponents of a fluid sample to provide achromatogram of the components of said fluid comprising:a source offluid to be analyzed and controllable fluid pump means in communicationwith said source of fluid; a source of eluent and eluent pump means incommunication with said source of eluent for pumping eluent through saidapparatus; first and second reservoir means for holding a diluted sampleof said fluid and an undiluted sample of said fluid, respectively; ionseparation means and ion detection means adapted to be placed incommunication with a selected one of said first and second reservoirmeans for receiving a fluid sample stored in said selected one of saidfirst and second reservoir means; means for mixing an undiluted sampleof said fluid with said eluent to provide said diluted fluid sample forstorage in one of said first and second reservoir means; and valve meansfor selectively switching said first and second reservoir means fromcommunication with said fluid pump means to communication with saideluent pump means for displacing fluid samples stored in said first andsecond reservoir means, respectively, through said detection means inpredetermined timed relationship.
 2. The apparatus set forth in claim 1including:valve means for conducting an undiluted fluid sample from saidfluid pump means to said mixing means and eluent from said source ofeluent to said mixing means for controlled mixing of fluid with saideluent to provide said diluted fluid sample.
 3. The apparatus set forthin claim 1 including:valve means for conducting fluid to said mixingmeans while filling one of said first and second reservoir means withsaid undiluted fluid sample.